In one color system, an array or series of different color imaging stations are aligned above an endless belt. Each imaging station contains a raster output scanner (ROS), photoreceptor drum, development station, and cleaning station. The ROS emits an electronic beam (laser) which impinges on the rotating photoconductive drum, thereby causing that location on the drum to undergo a change in electrical charge. As the drum continues to rotate past the development station, toner particles of a color which is unique to that imaging station will attach to the drum at the location charged by the ROS. This colored image is then transferred to an intermediate transfer belt that is passing by, and in contact with, the photoreceptor drum. As the intermediate belt passes by the different imaging stations (each usually containing a different color) it picks up subsequent color layers to create a complete color image which is then transferred to media.
Each colored beam must be in substantial registration with the other beams deposited on the belt for a final color copy. If any color needs to be re-aligned or skewed, the ROS unit is moved accordingly. In one embodiment there are also two sensors (Mark On Belt, or MOB sensors) that are fixed in position to a point on the machine frame, such that the colored images pass within view of these sensors. These sensors serve to detect the misregistration or misalignment between colors. The actuation of the deskew portion of the correction is performed via a ROS mechanism such as in of this invention. Each ROS unit has its own motor so that it could independently be skewed for image alignment. This type of color system having an array of ROS units is generally described in U.S. Pat. No. 6,418,286 and is incorporated by reference into this disclosure. As noted above, the color image deposited on the drum is subsequently deposited onto the belt. As the drum continues to rotate, it passes through the development station with a latent image which causes toner to stick to the drum where the electrical discharging (by the ROS) has taken place. The drum further rotates until the image is in contact with this intermediate transfer belt where the image is transferred from the drum to the belt. Each of the six or plurality of imaging stations deposits its own color and subsequently movement of the belt is moved past each of the imaging stations and allows each of the color separations to be deposited in turn. Thus, when the colors are out of alignment, the image needs to be skewed as does the image beam. By placing registration images side by side on the intermediate belt, the MOB sensors will indicate how much each ROS needs to be skewed to provide the optimum color-to-color registration deposited on the belt by the six or several ROS units.
One of the problems encountered is that the prior art mountings of the ROS are not robust to vibration sources within the imaging system, thereby causing “banding”. These prior art mountings are susceptible to vertical vibration which generally causes imprecise image deposition. By “banding” is meant a series of dark and light image lines causing image quality defects or color variations. The present invention involves an improved ROS mounting and skew adjustment mechanism. In typical prior art ROS mounting—the spheres and arms are located in the bottom portion of the ROS in line with the focal point of the ROS beam.
As noted above, generally, these prior art ROS mountings are positioned at the bottom lower end of the ROS, usually in the form of arms, one on each lower side of the ROS. Each arm is adjacent to a mounting sphere, which lie along the focal point axis. This allows the ROS to pivot about the focal axis without affecting focus itself. Reuse of this prior art configuration, especially in more compact future systems requires a need to locate the mounting spheres off axis. This presents a problem of how to mount the ROS such that it isn't overconstrained and has the degree of freedom needed to permit proper deskewings of the beam when necessary. For image registration purposes, the ROS beam needs to be deskewed in order to align its image with the image of the other colors being written on the belt.